Integrated audio amplification circuit with multi-functional external terminals

ABSTRACT

An audio amplification circuit may include an input terminal for receipt of an input signal from a transducer. A signal processor may be coupled to the input terminal for receipt and processing of the input signal to generate a processed digital audio signal in accordance with a programmable configuration setting of the signal processor. A serial data transmission interface is configured for receipt of the processed digital audio signal and supply of a corresponding digital audio stream at an output terminal of the integrated audio amplification circuit. A serial data receipt interface may be coupled to an externally accessible configuration terminal of the integrated audio amplification circuit and a controller is configured to adjust one of the programmable configuration setting of the signal processor and a format of a digital audio stream in accordance with first configuration data received through the serial data receipt interface.

The present invention relates in one aspect to an audio amplificationcircuit comprising an input terminal for receipt of an input signal froma transducer. A signal processor is operatively coupled to the inputterminal for receipt and processing of the input signal to generate aprocessed digital audio signal in accordance with a programmableconfiguration setting of the signal processor. A serial datatransmission interface is configured for receipt of the processeddigital audio signal and supply of a corresponding digital audio streamat an output terminal of the integrated audio amplification circuit. Aserial data receipt interface is operatively coupled to an externallyaccessible configuration terminal of the integrated audio amplificationcircuit and a controller is configured to adjust one of the programmableconfiguration setting of the signal processor and a format of a digitalaudio stream in accordance with first configuration data receivedthrough the serial data receipt interface. The controller is in a firststate is responsive to a logic state of the externally accessibleconfiguration terminal to control the format of the digital audio streamor the programmable configuration setting. In a second state, thecontroller is configured for receipt and reading of the firstconfiguration data through the externally accessible configurationterminal and the serial data receipt interface.

BACKGROUND OF THE INVENTION

Minimal size and a minimal number of external terminals or pins areimportant performance measures for integrated audio amplificationcircuits for application in miniature capacitor or condenser microphonessuch as ECM and MEMS condenser microphones. These types of condensermicrophones are designed for capture and processing of sound in numerousportable devices and applications such as mobile terminals, personalcomputers, hearing instruments, headsets, sound recording cameras etc.These miniature condenser microphones typically provide very limitedhousing space for accommodating integrated audio amplification circuits.

Furthermore, these applications are normally cost sensitive. Sincemanufacturing costs of an integrated semiconductor circuit are largelyproportional to the size of the integrated circuit, there is aconsiderable advantage in minimizing the number of pads or terminals ofthe integrated circuit due to the associated die area consumption.Likewise, simplification of audio signal processing and datacommunication interface circuitry of the integrated audio amplificationcircuit is also of considerable interest because this reduces die areaconsumption and therefore manufacturing costs as well. The datacommunication interface circuitry may comprise a programming interfaceallowing an external application processor, like a general purposemicroprocessor or Digital Signal Processor, to set or modifyprogrammable configuration settings of a signal processor or an audiooutput format of the integrated audio amplification circuit. Theprogramming interface allows the external application processor tocontrol operational characteristics of the integrated audioamplification circuit by changing the programmable configuration settingand adapt the operational characteristics to requirements of aparticular application or a particular operational state, e.g. a powerdown state.

Furthermore, there is a continued increase in the number of microphonesutilized in the portable devices. The application of multiplemicrophones is advantageous to support various types of sophisticatedaudio signal processing like stereo sound recording, beam-forming, windnoise cancellation etc. However, the use of multiple microphones inportable devices tend to increase the number of external datainput/output terminals, increase the amount of data wiring, increase thecomplexity of data transmission and receiving interfaces, increasecomplexity of associated data protocols etc. This is generallyundesirable because these factors tend to increase the size andmanufacturing costs of both the integrated audio amplification circuitsand the portable device in which the circuits are incorporated.

PRIOR ART

Existing microphone amplification circuits for miniature condensermicrophones comprise one or more externally accessible pads or terminalsthat can be used to set a static configuration setting of the microphoneamplification circuit. The static configuration setting is controlled bycoupling the external terminal(s) to a well-defined electrical potentialsuch as ground, or positive supply voltage, which selects a logic statewhich corresponds to the desired function. A controller of themicrophone amplification circuit is adapted to read the logic state orrespective logic states of the one or more externally accessibleterminals in connection with power-on. Based on the determined logicstates at power-on, the controller determines appropriate configurationsettings for the signal processor or data output format. Thereafter, theone or more externally accessible terminals remain inactive. The staticconfiguration setting may for example comprise a Left/Right setting ofthe audio output format of an I²S digital audio interface of a digitaloutput microphone amplification circuit. The I²S digital audio interfacetransmits a digital audio stream which comprises processed and digitizedrepresentations of a sound or audio input signal supplied by acapacitive transducer element of the miniature condenser microphone.Other static configuration settings may be a performance mode setting.

However, if it is desired to control a large number of parameters of thestatic configuration setting of the microphone amplification circuit bythis type of external terminal programming mechanism, the number ofexternally accessible terminals will rapidly reach an impractical numberfor the reasons outlined above. Hence, it would be desirable to enhancethe functionality of these externally accessible configuration terminalsby a dynamic mechanism which at one hand is compatible with known staticconfiguration setting techniques while at the other hand providingadditional interface functionality. This has been achieved in accordancewith a first aspect of the present invention wherein the externallyaccessible terminal in addition to its logic state based control of thestatic configuration setting of the signal processor of the microphoneamplification circuit also provides a serial data receipt interface. Theserial data receipt interface allows an external application processorto program the integrated audio amplification circuit by changing theprogrammable configuration setting. In a particular advantageousembodiment, the serial data receipt interface comprises an asynchronoussingle-wire data communication interface working according toestablished UART principles.

According to a second aspect of the present invention, a pair ofintegrated microphone amplification circuits is coupled in cascadebetween a general purpose I/O port of an external application processor,such as a programmable DSP, through a single wire data bus. The dataprotocol supports transmission and receipt of configuration data anddigital audio signals for both of the integrated microphoneamplification circuits through a single wire data bus so as to establisha very compact data communication interface with minimal use of externalpins/terminals and circuit board wiring.

SUMMARY OF THE INVENTION

A first aspect of the invention relates to an audio amplificationcircuit comprising an input terminal for receipt of an input signal froma transducer. A signal processor is operatively coupled to the inputterminal for receipt and processing of the input signal to generate aprocessed digital audio signal in accordance with a programmableconfiguration setting of the signal processor. A serial datatransmission interface is configured for receipt of the processeddigital audio signal and generation of a corresponding digital audiostream at an output terminal of the integrated audio amplificationcircuit. A serial data receipt interface is operatively coupled to anexternally accessible configuration terminal of the integrated audioamplification circuit and a controller is configured to adjust one ofthe programmable configuration setting of the signal processor and aformat of a digital audio stream in accordance with first configurationdata received through the serial data receipt interface. The controlleris in a first state is responsive to a logic state of the externallyaccessible configuration terminal to control the format of the digitalaudio stream or the programmable configuration setting. In a secondstate, the controller is configured for receipt and reading of the firstconfiguration data through the externally accessible configurationterminal and the serial data receipt interface.

The transducer preferably comprises a capacitive transducer element of acapacitive or condenser microphone wherein the transducer is responsiveto impinging sound on the microphone and generates a correspondingtransducer signal. The transducer signal is accordingly the input signalof the integrated audio amplification circuit. The capacitive microphonemay comprise a miniature ECM or a microelectromechanical (MEMS)condenser microphone shaped and sized for mobile terminal applications.

The signal processor preferably comprises preamplifier with adifferential or single-ended input coupled to the transducer through theinput terminal of the audio amplification circuit. A feedback networkmay be coupled between an output of the preamplifier and thesingle-ended or differential input. To minimize input signal loss inconnection with the loading of the capacitive transducer element, inputimpedance at the input of the preamplifier is preferably larger than 100MΩ, preferably larger than 1 GΩ, even more preferably larger than 10 GΩ,measured at 1 kHz.

The serial data transmission interface preferably comprises astandardized digital audio interface such as I²S, S/PDIF, AES/EBU,SLIMbus™ such that the digital audio stream is formatted in an industrystandard compliant manner which simplifies interoperability withexternal application processors such as a microprocessors and DSPs.Alternatively, the serial data transmission interface may operateaccording to be a proprietary data transmission protocol. In one suchembodiment, the serial data transmission interface transmits theprocessed digital audio signal directly to the output terminal forexample coded a one-bit pulse density modulated (PDM) signal streamoutputted by a sigma-delta analog-to-digital converter of the signalprocessor.

The first configuration data are utilized by the controller to controlthe programmable configuration setting of the signal processor. Theprogrammable configuration setting may be defined by respectiveparameter values stored in one or more configuration registersaccessible to the controller. The first configuration data comprisesthese parameter values. Initial values of the parameters may be storedin data memory area of the integrated audio circuit accessible to thecontroller. The controller may at power-on of the integrated audioamplification circuit be adapted to read configuration parameters for aninitial configuration setting of the signal processor from theconfiguration register if the configuration register comprisesnon-volatile memory. If the configuration register only comprisesvolatile memory, the configuration data may be written from the externalapplication processor to the controller in connection with systempower-on. The controller extracts configuration parameter values fromthe configuration data and writes these to the configuration registersuch that a desired configuration setting of the signal processor isloaded at power-on. The configuration parameter values held in theconfiguration register may be altered during normal operation of theintegrated audio amplification circuit by the external applicationprocessor. The external application processor can alter theconfiguration setting of the signal processor by transmittingconfiguration data with new parameter values to the controller of theaudio amplification circuit through its serial data receipt interface.The external application processor may generate and transmit the firstconfiguration data to the controller through a suitable serialcommunication interface connected to the serial data receipt interfaceof the integrated audio amplification circuit. The first configurationdata are preferably formatted by the external application processor inaccordance with a predetermined serial data protocol, preferably aprotocol that supports data communication through a single wire, e.g. aUART based data protocol. According to one such embodiment, thecontroller is configured for reading the first configuration dataformatted according to a serial data protocol comprising:

a pre-amble with a predetermined number of bits,

a register address of a configuration register of the programmableconfiguration setting of the signal processor,

a parameter value of the configuration register.

The data signal, carrying the first configuration data formattedaccording to the predetermined data protocol, is preferably encoded in asimple proprietary manner to provide a data signal which the externalapplication processor can generate with low computational overhead. Thedata signal may comprise a single-edge or double-edge pulse densitymodulated signal and the controller configured to read this single ordouble-edge pulse density modulated signal through the serial datareceipt interface. These types of single-edge and double-edge pulsedensity modulated signals may advantageously be generated by theexternal application processor through a general purpose I/O port ratherthan industry standard compatible data communication interfaces or portssuch as I²C, SPI interfaces etc. The use of such general purpose I/Oport for configuration data transmission is helpful in reducingcomputational resources involved in the handling of the above-mentionedrelatively complex industry standard data interfaces.

The externally accessible configuration terminal controls the formatselection of the digital audio stream and/or the programmableconfiguration setting of the signal processor during the first state ofthe controller in accordance with the present aspect of the invention.In addition, the externally accessible configuration terminal is coupledto the serial data receipt interface allowing receipt of the firstconfiguration data through the same pin or terminal in the second stateof the controller. In the second state the controller is insensitive tothe logic state of the externally accessible configuration terminal withrespect to the format selection of the digital audio stream and/or theprogrammable configuration setting. Consequently, the functionality ofthe externally accessible configuration terminal differs between thefirst and second controller states such that a single external terminalprovides multiple functions. This feature is beneficial because itreduces the number of external terminals or pads of the audioamplification circuit. This feature also reduces the amount ofelectrical wiring required to connect the audio amplification circuit toan external application processor such as a DSP. Furthermore, due to theprovision of the first controller state the audio amplification circuitremains at power-on responsive to the logic state of the externallyaccessible configuration terminal. Hence, allowing the present audioamplification circuit to operate in a backwards compatible manner with afunctionality similar to the above described prior art circuits withstatic configuration settings.

The format selection of the digital audio stream may be utilized inconnection with an I²S compliant serial data transmission interface orany other dual-channel transmission interface supporting a first datachannel and a second data channel. The controller may therefore beconfigured to encode the processed digital audio signal on the first orthe second data channel in accordance with the logic state of theexternally accessible configuration terminal during the first state.Hence, by selecting the logic state of the externally accessibleconfiguration terminal the controller may determine whether the digitalaudio stream is delivered in the left channel or right channel of I²Sframes of the digital audio stream. Thereby, a pair of identicalintegrated audio amplification circuits can be coupled to a shared I²Sbus and deliver a dual-channel or stereo digital audio stream to theexternal application processor.

In other embodiments, the selected logic state of the externallyaccessible configuration terminal is utilized to determine theprogrammable configuration setting of the signal processor. Theprogrammable configuration setting controls audio processingcharacteristics of the signal processor such as respective bias voltageand currents of amplification and integrator circuits of the signalprocessor, activation or interruption of signal processing circuits andelements, sampling frequency of an analog-to-digital converter, DC biasvoltage of voltage pumps etc. In one embodiment the programmableconfiguration setting controls a plurality of configuration parameterssetting the audio processing characteristics of the signal processorsuch that a particular performance mode out of several availableperformance modes of the signal processor is selected. The performancemodes may comprise a high performance mode and a reduced performancemode of the signal processor. The dynamic range of the signal processoris larger in the high performance mode than in the reduced performancemode albeit at the expense of higher power consumption. Hence, anapplication specific trade-off between performance and power consumptioncan be selected by selection of the logic state of the externallyaccessible configuration terminal.

The skilled person will understand that numerous mechanisms may be usedto switch the controller from the first state to the second state.According to a preferred embodiment, the controller is configured to:

select the first state for a predetermined time period in response topower-on of the integrated audio amplification circuit; and

automatically switch to the second state after expiry of thepredetermined time period. The power-on may conveniently be detected bythe controller from a state switching of a power-on-reset (POR) signalof the integrated audio amplification circuit. The setting of thepredetermined time period may be based on a suitable timer associatedwith the controller. The timer may be activated by the power-on resetsignal and indicate the end of the predetermined time period to thecontroller at timer expiry. Alternatively, the controller may beconfigured to detect activation of a clock signal. In this embodiment,the controller may select the first state for a predetermined timeperiod after receipt of the clock signal supplied through a clock inputterminal of the integrated audio amplification circuit. The controlleris preferably configured to automatically switch to the second state inresponse to expiry of the predetermined time period. The latter periodmay be controlled by the above-described timer. In yet anotherembodiment, the controller is also configured to select the first statefor a predetermined time period in response to power-on of theintegrated audio amplification circuit. However, in the presentembodiment, the controller switches to the second state in response toreceipt of the above mentioned clock signal supplied through the clockinput terminal. The clock signal may be a master clock signal of theintegrated audio amplification circuit that is supplied by the externalapplication processor. In this manner, the external applicationprocessor can control the duration of the predetermined time period bycontrolling a delay between the application of DC supply voltage to theintegrated audio amplification circuit and the on-set of the masterclock signal. The external application processor may furthermore alsocontrol the application of DC supply voltage to the integrated audioamplification circuit allowing for even more accurate control of theduration of the predetermined time period.

The controller is preferably configured for asynchronous reading of thefirst configuration data through the serial data receipt interface inthe second state of the controller. This simplifies the interfacebetween the external application processor and the integrated audioamplification circuit. In the alternative, the controller may beconfigured for synchronous reading of the first configuration datathrough the serial data receipt interface in the second state. Thisembodiment is particularly advantageous if the integrated audioamplification circuit already is coupled to the above-described clocksignal supplied by the external application processor.

Another aspect of the invention relates to semiconductor die orsubstrate comprising an audio amplification circuit according to any ofthe above described embodiments thereof. The semiconductor die ispreferably fabricated in a sub-micron CMOS semiconductor process toallow large scale manufacturing of the audio signal amplificationcircuit at very low costs.

A still further aspect of the invention relates to a miniaturecapacitive or condenser microphone comprising a capacitive transducerelement responsive to impinging sound to generate a correspondingtransducer signal at a transducer signal terminal. The integratedmicrophone amplification circuit in accordance with any of theabove-mentioned embodiments is operatively coupled to the transducersignal terminal via the input terminal of the circuit for receipt andprocessing of the transducer signal. The miniature capacitive microphonemay comprise an electrets condenser microphone (ECM) or amicroelectromechanical (MEMS) condenser microphone both preferablyshaped and sized for mobile terminal applications.

According to a fourth aspect of the invention there is provided anintegrated audio amplification circuit which comprises a serial datatransmission interface coupled to a data input terminal and a serialdata transmission interface coupled to a data output terminal. Theserial data transmission interface and the serial data transmissioninterface can preferably be coupled in cascade during a transparentstate thereof to allow passage of channel mode defining data from afirst integrated audio amplification circuit to a second daisy chainedintegrated audio amplification circuit in connection with power-on ofthe circuits. The serial data receipt interface and the serial datatransmission interface both support dual-channel data streams whichallow the first integrated audio amplification circuit to pass throughconfiguration data to a second audio amplification circuit encoded onone of the data channels.

According to this aspect of the invention the integrated audioamplification circuit comprising:

an input terminal for receipt of an input signal from a transducer,

a signal processor operatively coupled to the input terminal for receiptand processing of the input signal to generate a first processed digitalaudio signal in accordance with a configuration setting of the signalprocessor,

a serial data receipt interface operatively coupled to a data inputterminal for receipt of an incoming dual-channel data stream formattedin accordance with a predetermined serial data protocol, wherein theconfiguration data comprises at least one of first configuration dataassociated with the configuration setting of the signal processor andsecond configuration data associated with a second configuration settingof a second signal processor of a second integrated audio amplificationcircuit; said second integrated audio amplification circuit beingconnectable to the integrated audio amplification circuit via a serialdata transmission interface and a data output terminal;

the serial data transmission interface configured for transmission of anoutgoing dual-channel digital audio stream formatted in accordance withthe predetermined serial data protocol;

a controller configured to enter one of a first channel mode and asecond channel mode in accordance with a logic state of the data inputterminal at power-on of the integrated audio amplification circuit; saidcontroller being further configured to subsequently executing steps of:

reading the incoming dual-channel data stream received through theserial data receipt interface,

extracting the first and second configuration data from first and seconddata channels, respectively, of the incoming dual-channel data stream,

writing one of the first and second configuration data to aconfiguration register of the integrated audio amplification circuit inaccordance with the selected channel mode,

encoding the first processed digital audio signal on the first datachannel of the outgoing dual-channel digital audio stream,

encoding one of the second configuration data and the second processeddigital audio signal on the second data channel of the outgoingdual-channel digital audio stream in accordance with the selectedchannel mode.

The skilled person will understand that characteristics of certaincircuits of the present integrated audio amplification circuit such asthe input terminal, the input signal from the transducer, the signalprocessor, the first processed digital audio signal and theconfiguration setting of the signal processor, may be identical to thecorresponding features of the above discussed integrated audioamplification circuit in accordance with the first aspect thereof.

According to an preferred embodiment of the present integrated audioamplification circuit the serial data receipt interface and serial datatransmission interface comprises a transparent state coupling the datainput terminal to the data output terminal via an inverter for apredetermined time period in response to power-on of the integratedaudio amplification circuit. The controller is configured to read thelogic state of the data input terminal in the transparent state toselect one of the first and second channel modes. Furthermore, thetransparent state allow the logic state of the data input terminal ofthe first integrated audio amplification circuit at power-on to bepassed onto the data input terminal of the second daisy chainedintegrated audio amplification circuit in inverted format by a simplemechanism. For example by adding an inverter to an appropriate positionin the transparent data pathway between the serial data receipt andtransmission interfaces. Hence, the logic state of the respective datainput terminals of the first and second daisy chained integrated audioamplification circuits are opposite during the transparent state.Thereby, the controller of the second audio amplification circuit willselect an opposite channel mode relative to the channel mode selected bythe controller of the first audio amplification circuit.

The transparent state may be entered in response to a power-on-resetsignal of the integrated audio amplification circuit to exploit analready existing signal and eliminate additional hardware. Thetransparent state may be terminated in various ways for example inresponse to a clock signal supplied through a clock input terminal ofthe integrated audio amplification circuit. The latter mechanism willallow an external application processor such as a DSP to control thelength of the predetermined time period in a very efficient manner ifthe external application processor already supplies the clock signal tothe integrated audio amplification circuit. The transparent state may beterminated in response to on-set of the clock signal or after a certaindelay relative to the on-set of the clock signal. The delay may bedefined as a certain number of clock cycles of the clock signal etc.

The clock signal may function as a master clock signal of the integratedaudio amplification circuit such that a common type of existing clocksignal may be exploited. According to an alternative embodiment, thecontroller is configured to automatically terminate the transparentstate after expiry of the predetermined time period. The predeterminedtime period may be set e.g. by a dedicated or general purpose timeravailable to the controller or integrated together with the controller.

The predetermined serial data protocol of the incoming dual-channeldigital audio streams may comprise first and second unique preamblesindicating the first and second configuration data, respectively, to thecontroller. The first configuration data and/or the second configurationdata may comprise register addresses and corresponding configurationparameter values for the configuration setting of the signal processor.

Each of the incoming dual-channel digital audio stream and the outgoingdual-channel data stream preferably comprises a double-edge pulsedensity modulated data signal encoding the first data channel one of aleading edge and a trailing edge of the data signal and encoding thesecond data channel on an opposite edge. This is a proprietary type ofdata signal that can be efficiently generated by common types of generalpurpose ports of the external application processor with a lowcomputational overhead.

A final aspect of the invention relates to a sound processing assemblycomprising a circuit board. The circuit board comprises first and secondaudio amplification circuit according to any embodiments of the abovedescribed fourth aspect of the invention. A first data wire iselectrically connecting the data output terminal of the first audioamplification circuit to the data input terminal of the secondintegrated audio amplification circuit. A digital signal processorcomprises a first general purpose input-output (I/O) port operativelycoupled to the data input terminal of the first audio amplificationcircuit through a second data wire of the circuit board for transmittingthe incoming dual-channel serial data stream to the first audioamplification circuit in accordance with the predetermined serialprotocol; a second general purpose input-output port operatively coupledto the data output terminal of the second audio amplification circuitthrough a third data wire of the circuit board for receipt and read-inof the outgoing dual-channel digital audio stream supplied by the serialdata transmission interface of the second audio amplification circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described in more detail inconnection with the append drawings in which:

FIG. 1 is a schematic circuit diagram of an integrated microphoneamplification circuit according to a first embodiment of the invention,

FIG. 2 is a schematic circuit diagram of an integrated microphoneamplification circuit according to a first embodiment of the inventioncoupled to an external DSP processor,

FIG. 3 is a schematic circuit diagram of an integrated microphoneamplification circuit according to a second aspect of the inventioncoupled to an external DSP processor,

FIG. 4 is a detailed schematic circuit diagram of a logic circuitassembly of the controller according to the second embodiment of theinvention,

FIG. 5 is a schematic circuit diagram of a sound processing circuitassembly comprising a pair of cooperating integrated microphoneamplification circuits according to a second aspect of the invention,

FIG. 6A) illustrates how data communication is initialized on anexemplary asynchronous serial data protocol used by a single wiredual-channel serial data receipt interface and dual-channel serial datatransmission interface of the integrated microphone amplificationcircuit according to the second aspect of the invention; and

FIG. 6B) illustrates a single data frame structure of the exemplaryasynchronous serial data protocol in detail.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic drawing of an integrated microphone amplificationcircuit 101 according to a preferred embodiment of the invention coupledto a capacitive transducer element (not shown) held inside a miniaturecondenser microphone capsule 103. The integrated microphoneamplification circuit 101 may serve as an amplifying and digitizingfront-end of an associated DSP based sound processing circuit assemblyand system as described in further detail below in connection with FIGS.2 & 3. The integrated microphone amplification circuit 101 is preferablyfabricated or implemented on a single CMOS semiconductor die. Theskilled person will appreciate that the integrated microphoneamplification circuit 101 may be sized and shaped for placement in aminiature microphone housing or capsule of a variety of different typesof condenser microphones e.g. a micro-electromechanical (MEMS) condensermicrophone, e.g. shaped and sized for mobile terminal applications Theintegrated microphone amplification circuit 101 comprises a signalprocessor or signal conditioner 104 interfacing at its input side to theminiature condenser microphone capsule 103. The signal processor 104generates a processed digital audio signal, in accordance with aprogrammable configuration setting of the signal processor 104, andsupplies the processed digital audio signal to a serial audio datainterface 116. The serial audio data interface 116 may comprise anindustry standard I²S audio interface or proprietary audio interface.The signal processor 104 comprises a preamplifier 110 which has an inputterminal or node IN coupled to the capacitive transducer element (notshown) arranged inside the miniature condenser microphone capsule. Thepreamplifier 110 may be implemented as a non-inverting operationalamplifier to provide very large input impedance at the input node orterminal of the preamplifier 110. This is beneficial because capacitiveelectret or condenser transducer elements of miniature condensermicrophones such as MEMS condenser microphones or ECMs exhibit extremelylarge generator impedances, essentially corresponding to a capacitorwith a value between 0.5 and 2 pF. To avoid input signal loss, thepreamplifier input is preferably configured with input impedance largerthan 100 MΩ, preferably larger than 1 GΩ, even more preferably largerthan 10 GΩ, measured at 1 kHz. The signal processor 104 furthercomprises a sigma-delta analog-to-digital converter 112 coupled to anoutput of the preamplifier 110. The sigma-delta analog-to-digitalconverter 112 is configured to digitize an amplified and bufferedmicrophone signal delivered at an output of the preamplifier 110. Adecimation filter 114 is included to convert a one-bit pulse densityformatted signal stream of the sigma-delta analog-to-digital converter112 into the processed digital audio signal. The latter is preferablydelivered in multi-bit format, e.g. between 16 bits and 24 bits forexample at a sampling rate between 16 kHz and 48 kHz, to a serial audiodata interface 116 configured for receipt and formatting of theprocessed digital audio signal in accordance with a standardizedprotocol such as I²S, S/PDIF, AES/EBU, SLIMbus™ etc. Alternatively, theserial audio data interface 116 may be adapted to a proprietary dataprotocol. In one such embodiment, the one-bit pulse density modulated(PDM) signal stream outputted by the sigma-delta analog-to-digitalconverter 112 is conveyed directly to the external output terminal SD.Hence, the decimation filter 114 may be eliminated and the serial audiodata interface 116 configured as a bypass or transmission buffer withoutperforming any formatting of the processed digital audio signal. In thisembodiment, the outgoing digital audio stream is formed by anon-decimated or ‘raw’ PDM signal stream. The use of a PDM signal streamis explained in further detail below in connection with a system aspectwhere a pair of amplification circuits is daisy chained.

A digital audio stream encoding the condenser microphone signal isaccordingly delivered by the serial audio data interface 116 at theexternally accessible output terminal or pad SD of the integrated audioamplification circuit 101. The operation of digital logic of the signalprocessor 104 of the integrated audio amplification circuit 101 iscontrolled by a master clock signal input received through theexternally accessible terminal or pad SCLK. The master clock signal isgenerated by an external application processor for example aprogrammable Digital Signal Processor (DSP) coupled to the serial audiodata interface 116 through the output terminal SD and controllingconfiguration of the integrated audio amplification circuit 101 asdescribed below. The master clock signal may have a frequency between 1and 5 MHz for typical applications. Respective clock signals for thesigma-delta analog-to-digital converter 112 and the decimation filter114 are derived from the received master clock signal. Clock signals forthe I²S serial audio data interface 116 are also derived from the masterclock signal and audio samples of the digital audio stream deliveredsynchronously thereto through the output terminal SD. A supply voltageterminal V_(DD) is used for supplying power to the integrated audioamplification circuit 101. The nominal supply voltage will depend onrequirements of any specific application, but may be situated between1.5 V and 3.0 V DC for typical portable terminal applications. Theskilled person will appreciate that the amplification circuit 101 maycomprise additional hardware blocks for example a voltage pump forgeneration of a DC bias voltage for the associated miniature condensermicrophone. The integrated audio amplification circuit 101 comprises acontroller 120 which may comprise a hard-wired digital state machine,for example comprising customized combinatorial and sequential logiccircuitry, or a programmable microprocessor kernel, such as an ARM-core.The skilled person will appreciate that the controller 120 may comprisea combination of the hard-wired digital state machine and theprogrammable microprocessor kernel. The controller 120 is configured toadjust the programmable configuration setting of the signal processor104 and the format of the digital audio stream supplied through the I²Sin accordance with configuration data received through a serial datainterface coupled through an external L/R channel select pad or terminalL/R. The external L/R terminal additionally functions as an externalconfiguration terminal for selecting the format of the digital audiostream such that the audio data is delivered in either a left channel ora right channel of the I²S frame of the digital audio stream dependingon a logic state of the L/R terminal. Hence, a pair of identicalintegrated audio amplification circuits can be coupled to a shared I²Sbus and deliver dual-channel or stereo audio data to the Digital SignalProcessor (DSP). The above dual functionality of the L/R terminal isachieved by configuration or adaptation of the controller 120 where thecontroller has first and second states with different functionality. Inthe first state the controller 120 is responsive to the logic state ofthe L/R terminal while the controller is configured for receipt andreading of configuration data through a serial data interface coupled tothe L/R terminal in the second state. Hence, in the first state the L/Rterminal or pin functions similarly to existing microphone amplificationcircuits and the channel configuration of the circuit may be chosen byconnecting the L/R terminal to the appropriate electrical potentialthrough a suitable pull-up or pull-down resistance. However, the presentthe controller 120 includes the second state where the L/R terminalfunctions as data input terminal of the serial data interface. Theskilled person will appreciate that the serial data interface may be anasynchronous single-wire interface working according to established UARTprotocols requiring no further external configuration terminal(s) of theintegrated audio amplification circuit 101 to form the serial datainterface. The transition between the first and second states of thecontroller 120 may be effected in numerous ways. In a preferredembodiment, the controller 120 is configured to select the first statefor a predetermined time period in response to power-on of theintegrated audio amplification circuit 104 or amplification circuit 104and automatically switch to the second state after expiry of thepredetermined time period. The power-on may be detected by thecontroller 120 from a state or transition of a power-on reset signalsupplied by a reset generator of the circuit 104. The predetermined timeperiod may be set to a value between 0 and 500 milliseconds such asbetween 100 and 250 milliseconds. In this embodiment, the controller 120may be adapted to read the logic state of the L/R terminal in connectionwith a power up and configuration sequence of the amplification circuit104 and determine the appropriate configuration of the I²S formatteddigital audio stream. Once, this is done, the controller 120 proceedsautomatically to the second state where the controller 120 ignores thelogic state or state transitions of the L/R terminal for the purpose ofconfiguring the I²S formatted digital audio stream. The controllercomprises an asynchronous single-wire interface (not shown) workingaccording to established UART protocols which allows the controller toread the configuration data to define or change the programmableconfiguration setting of the signal processor 104. The state switchingbetween the first and second states in connection with power-on and theoperation of the asynchronous single-wire interface is described inadditional detail below in connection with a circuit diagram of the L/Rterminal interface circuitry of the controller of the second embodimentof the invention.

The configuration data may include one or numerous configurationparameters of the programmable configuration setting of the signalprocessor. Each configuration parameter of the programmableconfiguration setting is preferably stored in an individuallyaddressable register or memory address associated with the controller120. In a preferred embodiment, the configuration data are utilized toselect between at least two different power consumption settings of thesignal processor 104. In the first programmable configuration setting,the signal processor enters a first power mode which defines a firstpower consumption of the signal processor and in a second programmableconfiguration setting the signal processor enters a second power modewhich defines a second power consumption of the signal processor 104.The first power consumption is larger than the second power consumptionfor example 50% or 100% larger. The skilled person will appreciate thatthat the first power mode may be a normal operation mode where thesignal processor 104 works with nominal or full audio signal processingperformance. The second power mode may either be a reduced performancemode, where the microphone signal continues to be amplified, digitizedand outputted albeit with reduced performance compared to the firstpower mode. Alternatively, the second power mode may comprise a standbyor power-down mode where audio signal processing is interrupted. Thereduced performance mode may comprise a lower signal-to-noise ratioand/or, a lower bandwidth of the outputted digital audio stream. Thismay be achieved in numerous ways for example by controlling theappropriate parameters of certain configuration registers. Theseconfiguration registers may comprise volatile or non-volatile memorysuch as RAM locations or registers of the controller. The configurationregisters may hold respective configuration parameters defining currentsor voltages of active components and/or values of passive components ofthe signal processor 104. These include bias current settings ofintegrator stages of the sigma-delta analog-to-digital converter 112, aclock frequency of the sigma-delta analog-to-digital converter 112 andparameters defining bias current settings of the preamplifier 110 etc.

FIG. 2 is a simplified schematic circuit diagram of a sound processingcircuit assembly 200 which comprises the above disclosed integratedaudio amplification circuit 101. The sound processing circuit assembly200 may comprise a suitable carrier such as a printed circuit boardhaving various components such as the integrated audio amplificationcircuit 201 and the programmable DSP 202 attached thereon by solderingor any other suitable mounting technique like wire bonding etc. Theprogrammable DSP 202 comprises terminals V_(SS) and GND for receipt of apower supply voltage. The programmable DSP 202 comprises clock signalterminal CLK_MIC that supplies a master clock signal to the clock inputterminal or master clock input pad SCLK of the amplification circuit 201as discussed above. This master clock signal is generated by theprogrammable DSP 202 preferably by division from a system clock signalsupplied to the DSP 202 from a suitable clock generator (not shown). Theprovision of the master clock signal SLCK to the amplification circuit201 from the DSP 202 allows internal clock signals and data bits of theserial audio stream delivered through external terminal SD of theamplification circuit 101 to be synchronous to the clock of the DSP 202.The frequency of the master clock signal will vary according to therequirements for a particular application. The digital circuitry of theamplification circuit 201 is preferably configured for a nominal clockfrequency for example between 1 MHz and 10 MHz. In the presentembodiment, the digital audio stream transmitted by the amplificationcircuit 101 is formatted according to the industry standard I²S protocoland read by the DSP 202 through terminal SD_IN of its I²S interface. TheDSP 202 furthermore generates a serial data word select signal WS to theI²S serial audio data interface 116 of the amplification circuit 101 inaccordance with the I²S protocol. However, the skilled person willunderstand that other types of serial data protocols may be used fortransmission of the digital audio stream to the DSP 202 such as thepreviously discussed one-bit pulse density modulated (PDM) signalstream. The one-bit pulse density modulated (PDM) signal stream may besynchronized to the master clock signal supplied to the amplificationcircuit 101 on the externally accessible terminal SCLK.

A general output port GPIO1 of the DSP 202 is coupled to the externalL/R channel select terminal or L/R terminal of the amplification circuit101 through suitable electrical wiring on the carrier. The logic stateof the L/R terminal can either be set to logic high or logic low byappropriately coupling the L/R terminal to one of the illustratedpull-up and a pull-down resistors R_(UP) and R_(DOWN), respectively. Toensure that the logic state of the L/R terminal is unaffected by theport impedance of the general purpose output port GPIO1, the latter istri-stated (a high-impedance state) by the DSP 202 during power-on ofthe amplification circuit 101. Thereby, the logic state of the L/Rterminal initially becomes controlled by either the pull-up or pull-downresistor. The controller 120 select the first state for thepredetermined time period in response to receipt of the power-on of theamplification circuit 104 as described above. Thereafter, the controllerautomatically switches to the second state where it is able to readconfiguration data written by the DSP 302 from the general purposeoutput port GPIO1 through the serial data interface of the controller120 operatively coupled to the L/R terminal. The switch from the firststate to the second state may be based on a suitable timer of thecontroller 120 activated by the power-on reset signal. The timer expiresat the end of the predetermined time period. In an alternativeembodiment, the switch from first state to the second state iscontrolled by an initial clock pulse of the master clock signaldelivered to the controller as discussed below in additional detail inconnection with a second aspect of the invention. Each resistance valueof the pull-up and pull-down resistors R_(UP) and R_(DOWN),respectively, is preferably much larger than an output impedance of thegeneral purpose output port GPIO1. In this manner, the general purposeoutput port GPIO1 is capable of effectively controlling the binary datavalues on the L/R configuration terminal in the second state. Theresistance values of each of the pull-up and pull-down resistors may belarger than 100 kΩ, such as between 100 kΩ and 10 MΩ, such that anoutput impedance in the order of a few kΩ or less of the general purposeoutput port GPIO1 will allow the latter to control the voltage on theconfiguration terminal and associated wiring. The serial programminginterface comprises an asynchronous single-wire interface workingaccording to UART principles allowing the transmission of theconfiguration data to the controller 120 without occupying any externalpads or terminals of the amplification circuit 101. Furthermore, thesingle wire interface and the exploitation of the UART based serial datainterface minimize consumption of hardware and software resources on theDSP 202. This is because a data protocol on the asynchronous single-wireinterface can be very simple leading to a small consumption of hardwareand software resources on the DSP 202 in handing this data interface.Furthermore, the above serial programming interface unloads other typesof industry standard data communication ports and interfaces of the DSP202 such as SPI, IIC etc.

FIG. 3 is a simplified schematic circuit diagram of a sound processingcircuit assembly 300 according to a second aspect of the invention. Thesound processing circuit assembly 300 comprises an integrated audioamplification circuit 301 in accordance with a second embodiment inwhich the I²S digital audio interface discussed above has been replacedby a customized serial data transmission interface comprising I/Ocircuit 316. The customized serial data transmission interface isconfigured for handling a dual-channel digital audio stream carryingboth configuration data and processed digital audio signals. The soundprocessing circuit assembly 300 may comprise a suitable carrier such asa printed circuit board having various components such as the integratedaudio amplification circuit 301 and the programmable DSP 302 attachedthereon by soldering or any other suitable mounting techniques like wirebonding etc. The programmable DSP 302 comprises terminals V_(SS) and GNDfor receipt of a power supply voltage. The programmable DSP 302comprises clock signal terminal CLK_MIC that supplies a master clocksignal to the clock input terminal or master clock input pad SCLK of theamplification circuit 301 as discussed above. This master clock signalis generated by the programmable DSP 302 preferably by division from amaster clock signal of the DSP 202 such that internal clock signals anddata bits of the serial audio stream through external terminal PDM_DATAof the amplification circuit 301 are synchronous to the master clocksignal supplied by the DSP 302. The frequency of the master clock signalwill vary according to the requirements for a particular application.The digital circuitry of the amplification circuit 301 is preferablyconfigured for a nominal clock frequency for example between 1 MHz and10 MHz.

A general purpose I/O port GPIO1 of the DSP 302 is coupled to theexternal L/R channel select terminal or L/R terminal of theamplification circuit 301 through suitable wiring on the carrierschematically illustrated by data wire 321. A serial data receiptinterface forms part of the logic circuit assembly 323 of a controller320 and provides the interfacing to the external L/R terminal. Thecontroller 320 may comprise a hard-wired digital state machine forexample comprising customized combinatorial and sequential logiccircuitry embodied on an ASIC or a programmable microprocessor kernel,such as an ARM-core. The logic state of the L/R terminal can either beset to logic high or logic low by appropriately coupling the L/Rterminal to one of the illustrated pull-up and a pull-down resistorsR_(UP) and R_(DOWN), respectively, as discussed above. To ensure thatthe logic state of the L/R terminal is insensitive to the port impedanceof the general purpose I/O port GPIO1, the latter is tri-stated(high-impedance state) by the DSP 302 during power-on of theamplification circuit 301. Hence, the logic state of the L/R terminalmay initially be controlled by the selected one of the pull-up andpull-down resistors. In the alternative, the logic state of the L/Rterminal may be controller by the general purpose I/O port GPIO1 forexample according to a system initialization program executed by the DSP302. The controller 320 selects a transparent state of the serial datatransmission interface and the serial data receipt interface for apredetermined time period in response to receipt of the power-on of theamplification circuit 301. In this transparent state the controllerreads the logic state of the logic state of the external L/R terminaland enters a either a first channel mode or a second channel mode inaccordance with the detected logic state as explained in detail below inconnection with FIG. 4. The subsequent switching to a non-transparentstate of the controller 320 where the controller reads the configurationdata transmitted from the DSP 302 through the general purpose I/O portGPIO1 is carried out by a different mechanism than the previouslydiscussed timer controlled mechanism. In the present embodiment, theswitching from the transparent state to the second state is carried outby on-set of the master clock signal supplied to the controller 320through clock wire 322 and the master clock input pad SCLK. This isexplained in further detail below in connection with FIG. 4. The DSP 302is configured to generate and transmit a dual-channel digital audiostream through the general purpose I/O port GPIO1 to the controller 320.The dual-channel digital audio stream transmitted to the controller 302comprises both first configuration data, defining a configurationsetting of the signal processor 304, and second configuration datadefining a configuration setting of another signal processor of anotheror second integrated audio amplification circuit (not shown) coupled tothe integrated audio amplification circuit 301 through the customizedserial data transmission interface and the output terminal PDM data. Thefirst and second configuration data are encoded on different channels ofthe dual-channel digital audio stream. By evaluating its channel mode,the controller 320 determines which of the first and secondconfiguration data that are addressed to the amplification circuit 301,extracts the appropriate configuration data, and encodes the residualconfiguration data onto the second channel of the outgoing dual-channeldigital audio stream through output terminal PDM data. This featureenables the controller of the second integrated audio amplificationcircuit to read and extract the second configuration data. Thecontroller 320 writes the extracted configuration data targeted for thesame circuit to an appropriate configuration register or registersthrough the schematically illustrated data bus or wire 328 for storage.Finally, the controller 320 proceeds to a read processed digital audiosignal supplied by the signal processor 304 through data wire 325. Thecontroller encodes and adds the processed digital audio signal on theunused channel (the channel of the incoming dual-channel data streamthat contained the first configuration data) of the outgoingdual-channel digital audio stream. These features are explained inadditional detail below in connection with FIG. 4 and FIG. 5 thatillustrate the interconnection between the DSP 302 and a pair ofcooperating cascaded integrated audio amplification circuits 301, 303through a single wire data bus structure.

FIG. 4 is a detailed schematic circuit diagram of the logic circuitassembly 323 comprising the above-mentioned serial data transmissioninterface and serial data transmission interface both connected to thecontroller 320. The serial data transmission interface of the logiccircuit assembly 323 comprises a latch 309 with a data input X connectedto the external L/R terminal and an enable input connected to a dataoutput Q of a standard type of asynchronous reset synchronous set D-FF305. The reset input of the D-FF 305 is connected to a power-on-resetsignal POR of the integrated microphone amplification circuit 301. Aclock input of the D-FF 305 is connected to the master clock signal SCLKof the integrated microphone amplification circuit 301. The skilledperson will understand that the logic level of the L/R terminalpreferably is controlled by the GPIO1 port of the DSP 302 during thetransparent state of the serial data transmission interface and serialdata transmission interface in connection with power-on of theintegrated microphone amplification circuit 301. Thereby, the initialset logic level of the L/R terminal defines the L/R channel modeallocation of the integrated microphone amplification circuit 301. Thelogic circuit assembly 323 functions at power-on of the integratedmicrophone amplification circuit 301 to retain the latch 309 in atransparent state by asserting the enable input EN from the Q output ofthe D-FF 305. In this manner, data content on the L/R terminal,including its logic state or state transitions, is transmitted directlyto the output Q of the latch 309. The output Q of the latch 309 is readby the controller 320 as it represents the logic state of the L/Rterminal at power-on of the integrated circuit 301. The output Q of thelatch 309 is also coupled to a first input of a multiplexer 311 throughan inverter 329 such that the opposite logic state to that of the outputof latch 309 is passed through to the output of the multiplexer 311. Themultiplexer output is selected by the L/R phase signal driven by the Qoutput of the D-FF 305. Hence, the opposite logic state to that of theoutput Q of the latch 309 is passed onto the PDM data wire 324 duringthe transparent state and transmitted to the serial data receiptinterface of a second integrated microphone amplification circuit 303(refer to FIG. 5). Hence, the controller of second integrated microphoneamplification circuit 303 will, in connection with power-on, configurethe second integrated microphone amplification circuit 303 in theopposite channel mode to that of the first integrated microphoneamplification circuit 301.

The switching of the controller 320 from the transparent state to thenon-transparent state is controlled by the on-set of the master clocksignal SCLK in the present embodiment. The first clock pulse of themaster clock signal after the power-on-reset signal POR has beende-asserted clocks the “1” logic level applied to the D input of theD-FF 305 to its output Q leading to disablement of the latch 309. Thedisablement of latch 309 terminates the transparent state. The skilledperson will appreciate that the transparent state of the serial datatransmission interface and serial data transmission interface alsosupports other methodologies of setting the respective modes of thefirst and second integrated microphone amplification circuit 301, 303.This because various types of mode setting data and commands may beencoded in the dual-channel digital audio stream transmitted by the DSP302 from port GPIO1 and passed through the serial data interfaces of thefirst integrated microphone amplification circuit 301 and onto the daisychained or cascaded second integrated microphone amplification circuit303 during the transparent state, i.e. until arrival of the first clockpulse of the master clock signal as discussed above. The secondintegrated microphone amplification circuit is connected in series withthe present integrated microphone amplification circuit 301 through thePDM data line 324 and the associated external data terminal PDM Data.This is explained in additional detail in connection with FIG. 5 below.

The multiplexer 311 has a second input coupled to an outgoingdual-channel digital audio stream PDM OUT generated by the controller320. A select signal of the multiplexer 311 is coupled to the enableinput of the latch 309 as previously described. Once the non-transparentstate is entered, the Q output of the D-FF 305 forces a change of thelogic state of the multiplexer select signal such that the multiplexer311 switches to pass the outgoing dual-channel digital audio stream PDMOUT to the external data terminal PDM data instead of the data signal onthe latch output Q. The outgoing dual-channel digital audio stream isgenerated by the controller 320 in the non-transparent state thereof.The present integrated microphone amplification circuit 301 is placedclosest to the GPIO1 port of the DSP 302 and the first channel of theoutgoing dual-channel digital audio stream therefore comprises theprocessed digital audio signal generated by the signal conditioner 304while the second channel comprises the extracted second configurationdata for second amplification circuit 303 as discussed above. Theskilled person will appreciate that the data contained in an outgoingdual-channel digital audio stream of the second integrated audioamplification circuit 303 differs because the latter circuit isconfigured as right channel mode as described in detail below inconnection with FIG. 5.

In yet another embodiment of the invention, the L and R channel modes ofthe amplification circuits are detected by each controller from observedpreamble data content of the respective incoming dual-channel serialdata streams received through the respective L/R terminals. Inconnection with power-on of the first and second amplification circuits,the DSP 302 transmits a unique pre-amble on each of the first and secondchannels of the dual-channel serial data streams. The pre-amble isorganized such that it is distinguishable from the first and secondconfiguration data and from the first and second processed digital audiosignals. The pre-amble may be a rare PDM data pattern, preferablyrepeated, to decrease the likelihood of the pattern is contained innormal processed digital audio signals. The preambles associated withthe left/L and right/R modes of the amplification circuits must bedifferent, such that each controller can determine the appropriate leftor right mode of its amplification circuit. The L and R mode selectionsare preferably carried out by a procedure where the controller of thefirst amplification circuit 301 detects whether received preamble datafrom the DSP 302 comprises both the first and second preambles. If thatis the case, the controller concludes the amplification circuit 301 isset to L mode in the present embodiment. The controller of the firstamplification circuit 301 proceeds to extract and write the firstconfiguration data to the first configuration register(s) as describedabove. The controller of the first amplification circuit 301 proceeds toextract the second preamble and second configuration data and encodethese on the second channel of the dual-channel digital audio streamtransmitted by the first amplification circuit 301 to the secondamplification circuit 303 through the data output terminal SD and datawire 507.

The logic circuit assembly 323 also comprises the serial data receiptinterface connected to the external L/R terminal of the integratedmicrophone amplification circuit 301. The serial programming interfaceis an asynchronous single-wire data interface operating according toUniversal Asynchronous Receiver/Transmitter (UART) principles. Theserial programming interface comprises D-FF 307, low-pass filter 313 andUART 315. The incoming dual-channel data stream on the external L/Rterminal is applied to the data input D of the D-FF 307 and clocked tothe Q output by the master clock signal connected to the clock input ofthe D-FF 307. The first and second configuration data, or the firstprocessed digital audio signal and the second configuration data,depending on the arrangement of the circuit 301 in the circuit cascade,are extracted bit by bit from the incoming dual-channel data stream bythe low-pass filter 313. The low-pass filter 313 may have a cut-offfrequency corresponding to about 10-50 clock cycles of the master clocksignal to extract the incoming configuration data and processed digitalaudio signal if these are encoded as the below discussed double-edgepulse density modulated data signal. The UART 315 extracts or separatesthe first and second configuration data, or the first processed digitalaudio signal and the second configuration data from the incoming datastream in accordance with the selected data protocol as described infurther detail below in connection with FIG. 6. These configuration dataand/or processed digital audio signal are transmitted to the controllervia configuration data wire 228 and processed in the controller as partof generating the data content of the outgoing dual-channel digitalaudio stream in dependence on the selected channel mode as described infurther detail below.

FIG. 5 is a simplified schematic circuit diagram of a sound processingcircuit assembly 500 comprising the previously discussed cooperating anddaisy-chained pair of integrated audio amplification circuits 301, 303of the same type, but configured in L channel mode and R channel mode,respectively, by the above-described channel assignment mechanism duringthe transparent states of the circuits. The pair of integrated audioamplification circuits 301, 303 are coupled to the previously discussedprogrammable DSP 302 via the first general purpose output port GPIO1 andthe second general purpose output port GPIO2 as discussed above. Theprogrammable DSP 302 may in some applications be replaced with anothertype of external application processor such as a general purposemicroprocessor, microprocessor core etc. The sound processing circuitassembly 500 may comprise a suitable carrier (not shown) such as aprinted circuit board having various components such as the data signalwiring, first and second integrated audio amplification circuits 301,303, respectively, and the programmable DSP 302 integrated or attachedthereon by soldering or other mounting techniques like wire bonding etc.Each of the first and second integrated audio amplification circuits301, 303, respectively, comprises an externally accessible data inputterminal, using existing respective L/R configuration terminals in thepresent embodiment, which are connected in cascade through theexternally accessible data output terminal PDM Data of the firstintegrated audio amplification circuit 301. The programmable DSP 302comprises the clock signal output terminal CLK_MIC that suppliessubstantially identical master clock signals to the clock inputterminals SCLK of the first and second integrated audio amplificationcircuits 301, 303, respectively, as discussed above. Furthermore, theprogrammable DSP 302 generates and transmits the previously discussedconfiguration data, which comprises both first and second configurationdata formatted as prescribed by the predetermined data protocol, throughthe first general purpose output port GPIO1 connected to the firstamplification circuit 301 through a single data wire 505. The secondgeneral purpose 10 port GPIO2 is used for receiving and reading thefirst and second digital audio signals encoded on the first and secondchannels, respectively, of an outgoing dual-channel digital audio streamtransmitted from the external PDM Data output terminal of the secondamplification circuit 303 (RIGHT MIC). Hence, the respective serial datatransmission and receipt interfaces of first and second amplificationcircuits 301, 303 are effectively coupled in cascade between the generalpurpose output and input ports GPIO1 and GPIO2 of the programmable DSP302. In this manner, the respective configuration data can betransmitted to the first and second amplification circuits 301, 303 andthe respective processed digital audio signals generated by the firstand second amplification circuits 301, 303 transmitted to the DSP 302through the illustrated single wire data bus.

The single wire data bus occupies only two externally accessibleterminals of each of the first and second amplification circuits 301,303. The skilled person will appreciate that the first and secondintegrated audio amplification circuits 301, 303 may be coupled torespective condenser microphones (not shown) in a manner similar to theone discussed above in connection with the amplification circuit 101 ofFIG. 1. In response to sound on the condenser microphones, the first andsecond integrated audio amplification circuits may therefore supplyfirst and second processed digital audio signals, respectively,representing the sound such as speech and music. The first and secondprocessed digital audio signals are transmitted through the respectiveserial data transmission interfaces and associated data wiring 507, 509.Each of the serial data transmission interfaces is configured forgeneration of the previously discussed dual-channel digital audio streamoutputted through the respective externally accessible data outputterminals PDM Data. In the outgoing dual-channel digital audio streamcarried on the first data wire 507 the first channel encodes the firstprocessed digital audio signal supplied by the signal processor of theamplification circuit 301 (LEFT MIC) and the second channel encodes thesecond configuration data for the second amplification circuit 303. Inthe dual-channel digital audio stream carried on the second data wire509, the first channel still encodes the first processed digital audiosignal while the second channel encodes the second processed digitalaudio signal supplied by the signal processor of the secondamplification circuits 303 instead of the second configuration data.

The type of data encoded on the incoming dual-channel data streamsreceived by the first and second amplification circuits 301, 303 differsduring normal operation of the assembly 500 due to their differentpositions in the cascade arrangement of the circuits 301, 303. Thecontroller of the first amplification circuit 301 reads and extractsboth the first configuration data, for the first amplification circuit301 and second configuration data for the second amplification circuit303 from the incoming dual-channel data stream. The controller of thefirst amplification circuit 301 is configured in R channel mode andproceeds therefore to extract the first configuration data, which areassociated with the configuration setting of the signal processor of theRIGHT MIC circuit 301 in the present exemplary embodiment, from thereceived configuration data. The controller writes the firstconfiguration data to either a configuration register which controls theconfiguration setting of the signal processor or a suitable data memoryarea for later loading into the configuration register. The controllerthereafter proceeds to generate the outgoing dual-channel data stream inaccordance with the set R channel mode. The controller reads the firstprocessed digital audio signal from the signal processor as describedabove and formats the first processed digital audio signal and thealready extracted second configuration data and formats these inaccordance with the serial data protocol. The first processed digitalaudio signal is encoded on the vacant first data channel, i.e. vacantbecause the first configuration data have been extracted, of theoutgoing dual-channel data stream while the second configuration dataare encoded on the second data channel of the outgoing dual-channel datastream.

The controller of the second amplification circuit 303 proceeds toreading the incoming dual-channel data stream through the serial datareceipt interface coupled to the external L/R terminal of the secondamplification circuit 303. The controller of the second amplificationcircuit 303 is configured in L channel mode and proceeds therefore toextract the first processed digital audio signal from the first datachannel and the second configuration data from the second data channel.The latter configuration data are associated with the configurationsetting of the signal processor of the LEFT MIC circuit 303 in thepresent exemplary embodiment. The controller writes the secondconfiguration data to either a configuration register which controls theconfiguration setting of the signal processor or to a suitable datamemory area for later loading into the configuration register. Thecontroller thereafter proceeds to generate the outgoing dual-channeldata stream in accordance with the set L channel mode. The controllerreads the second processed digital audio signal supplied by the signalprocessor of the LEFT MIC circuit 303. The controller formats the secondprocessed digital audio signal and the already extracted first digitalaudio signal in accordance with the serial data protocol. The firstprocessed digital audio signal is once again encoded on the first datachannel of the outgoing dual-channel data stream while the secondconfiguration data are encoded on the vacant second data channel, i.e.because the second configuration data have been extracted by thecontroller of the second circuit 303. Hence, the outgoing dual-channeldata stream is effectively a dual-channel digital audio stream which issent through the serial data transmission interface of the secondamplification circuit 303 for transmission to the second general purposeI/O port GPIO2 of the DSP 302 through the data wire 509.

As mentioned above, the various outgoing and incoming dual-channel datastreams are preferably formatted according to the serial data protocolexplained below in connection with FIG. 6. The various outgoing andincoming dual-channel data streams are preferably encoded as double-edgepulse density modulated signals in which the first data channel isencoded on a rising or falling edge of the data signal and the seconddata channel is encoded on the opposite edge of the data signal. Theskilled person will appreciate that the first and second configurationdata, the first and second processed digital audio signals aretransmitted between the programmable DSP 302 and the first and secondamplification circuits 301, 303, respectively, using only a single datawire bus which establish a very compact data communication interfacewith minimal use of external pins/terminals and board wiring. Theskilled person will appreciate that even the master clock signaldistributed to the respective SCLK inputs of the first and secondamplification circuits 301, 303 does not add overhead to the presentsingle wire data communication interface because the master clock signalis necessary for other purposes in the digital circuitry of theamplification circuits.

FIG. 6A) illustrates how data communication is initialized on anexemplary asynchronous serial data protocol of the above discusseddual-channel serial data streams allowing the exchange of both digitalaudio data and configuration data between the DSP 302 and the first andsecond amplification circuits 301, 303 through the above-discussedsingle wire data interface or data bus comprising data wires 505, 507and 509. The upper graph 601 shows the dual-channel serial data line orwire PDM Data while the lower graph 603 shows the master clock signalapplied to the first and second amplification circuits 301, 303 throughthe externally accessible terminal or pad SCLK. The transmission of aserial data frame is started or initialized by holding the PDM Data lineat a fixed logic state for N clock cycles of the master clock and thenswitching the PDM Data line to an opposite logic state. FIG. 6B)illustrates a single data frame of the exemplary asynchronous serialdata protocol to explain the protocol details. The depicted data framecomprises a preamble of 8 bits which is used to synchronise the serialdata communication channel as the bit rate of the channel is initiallyunknown and a symbol clock rate is required. The preamble is followed bya host address, e.g. 7 bits, which is used to select or address eitherthe first or the second amplification circuit. The host address isfollowed by a read/write indicator in respect of the data content ofcurrent frame and an acknowledge bit, ACK. The acknowledge bit isfollowed by the above-mentioned data content of the data frame andgraphically illustrated as a single byte, DATA, comprising 8-bits ofdata. The data content of the frame preferably comprises a plurality ofdata bytes in accordance with the specific details of the selected framestructure of the serial data protocol. The data content may comprise afirst byte with a register address and a one or more subsequent databyte(s) holding a register value to be written to the register addressin question or alternatively to be read from the register address inquestion. The register value may set a particular configurationparameter of the signal processor of the selected amplification circuit.The skilled person will appreciate that each of the amplificationcircuits 301, 303 may comprise a plurality of configuration registerswith associated pairs of register addresses and register values to setmultiple configuration parameters. The multiple configuration parametersmay in combination define the programmable configuration setting of thesignal processor e.g. select a particular power mode. A secondacknowledge bit is inserted after the data content. During writing ofdata to the amplification circuit, the end of the data frame is signaledor marked to the controller by transmission of a post-amble byte with acertain bit pattern, POST-AMPLE, as illustrated. During reading of thedata content of the configuration register of the amplification circuit,the non-acknowledge bit, NACK, can be used by the controller to indicateto the master device that the intended data reading was unsuccessful.The skilled person will understand that the each configuration registermay comprise various forms of volatile and/or non-volatile memory suchas registers, data RAM, EEPROM, flash memory etc. for either temporaryor permanent storage of the received configuration parameter values. Theindividual data bits of the transmitted PDM data stream are preferablyManchester encoded because this simplifies clock less data recovery, orpossibly the design of clock recovery circuits, because the encodingalways provides at least one clock edge per data bit.

The invention claimed is:
 1. An integrated audio amplification circuitcomprising: an input terminal for receipt of an input signal from atransducer, a signal processor operatively coupled to the input terminalfor receipt and processing of the input signal to generate a processeddigital audio signal in accordance with a programmable configurationsetting of the signal processor, a serial data transmission interfaceconfigured for receipt of the processed digital audio signal andgeneration of a corresponding digital audio stream at an output terminalof the integrated audio amplification circuit, a controller configuredto adjust one of the programmable configuration setting of the signalprocessor and a format of the digital audio stream in accordance withfirst configuration data received through the serial data receiptinterface; wherein in a first state the controller is responsive to alogic state of the externally accessible configuration terminal tocontrol at least one of the format of the digital audio stream and theprogrammable configuration setting, in a second state the controller isconfigured for receipt and reading of the first configuration datathrough the externally accessible configuration terminal and serial datareceipt interface, wherein the controller is configured to select thefirst state for a predetermined time period in response to power-on ofthe integrated audio amplification circuit and automatically switch tothe second state after expiry of the predetermined time period, furtherwherein the controller is configured to read double-edge pulse densitymodulated configuration data through the serial data receipt interface,a leading edge or a trailing edge of the double-edge pulse densitymodulated configuration data used to encode the first configuration datafor the integrated audio amplification circuit, and an opposite edge ofthe dual-edge pulse density modulated configuration data used to encodesecond configuration data for another integrated audio amplificationcircuit connectable to the output terminal for receipt of the digitalaudio stream.
 2. The integrated audio amplification circuit according toclaim 1, wherein the controller is configured to: select the first statefor a predetermined time period after receipt of a clock signal suppliedthrough a clock input terminal of the integrated audio amplificationcircuit; and automatically switch to the second state after expiry ofthe predetermined time period.
 3. The integrated audio amplificationcircuit according to claim 1, wherein the controller is configured to:select the first state for a predetermined time period in response to apower-on signal of the integrated audio amplification circuit; andswitch to the second state in response to receipt of a clock signalsupplied through a clock input terminal of the integrated audioamplification circuit.
 4. The integrated audio amplification circuitaccording to claim 1, wherein the power-on of the integrated audioamplification circuit is indicated by a power-on-reset signal.
 5. Theintegrated audio amplification circuit according to claim 1, wherein thecontroller is configured for asynchronous reading of the firstconfiguration data through the serial data receipt interface in thesecond state.
 6. The integrated audio amplification circuit according toclaim 1, wherein the controller is configured for synchronous reading ofthe first configuration data through the serial data receipt interfacein the second state based on an incoming clock signal applied to a clockinput terminal of the integrated audio amplification circuit.
 7. Theintegrated audio amplification circuit according to claim 1, wherein thecontroller is configured for reading the first configuration dataformatted in accordance with a predetermined serial data protocol; theserial data protocol comprising: a pre-amble with a predetermined numberof bits, a register address of a configuration register of theprogrammable configuration setting of the signal processor, a parametervalue of the configuration register.
 8. The integrated audioamplification circuit according to claim 1, wherein the serial datatransmission interface is configured for generation of a dual-channeldigital audio stream comprising a first data channel and a second datachannel; the controller being configured to encode the processed digitalaudio signal on the first or the second data channel in accordance withthe logic state of the external configuration terminal during the firststate.
 9. The integrated audio amplification circuit according to claim1, wherein the programmable configuration setting of the signalprocessor comprises: a first power mode set by one or more configurationparameters of the first configuration data defining a first powerconsumption of the signal processor, a second power mode set by the oneor more configuration parameters defining a second power consumption ofthe signal processor; wherein the first power consumption is larger thanthe second power consumption.
 10. The integrated audio amplificationcircuit according to claim 1, wherein the signal processor comprises: asigma-delta analog-to-digital converter configured to supply theprocessed digital audio signal to the serial audio data interface. 11.The integrated audio amplification circuit according to claim 1, whereinthe input impedance at the input terminal is larger than 10 GΩ, measuredat 1 kHz.
 12. The A semiconductor die or substrate comprising an audioamplification circuit according to claim
 1. 13. A sound processingcircuit assembly comprising: an audio amplification circuit according toclaim 1; a digital signal processor comprising: a first general purposeinput-output port operatively coupled to the configuration terminal ofthe audio amplification circuit for transmitting the serial data streamcomprising the first configuration data thereto, a second generalpurpose input-output port operatively coupled to the output terminal ofthe audio amplification circuit for receipt and reading of the digitalaudio stream generated by the audio amplification circuit.
 14. The soundprocessing assembly according to claim 13, comprising: one of a pull-upresistance and a pull-down resistance coupled from the configurationterminal to a predetermined electric potential to set a logic state ofthe configuration terminal during the first state; and the first generalpurpose input-output port of the digital signal processor comprising atri-state output driver.